math
posted by math .
The graph below shows the rate of natural gas usage (in therms per day) in one household for a 30  day period. Estimate the total number of therms used during this period. Use left endpoints and rectangles with widths of 3 days.
View graph at:
postimg.o rg/image/61nw3co3r/
I came up with ans 165.

it's ok. I got it now.